Theresa A. Tuthill

Volume flow measurement using doppler and grey-scale decorrelation

A technique for volumetric blood flow measurement was developed by combining standard Doppler measurements with grey-scale decorrelation. Steered Doppler is used to determine the in-plane velocities, which are then used to extract the out-of-plane velocities from the temporal A-line decorrelation. As a result, a three-dimensional (3-D) vector flow field can be computed over the imaging plane using a single clinical transducer without knowledge of the vessel orientation. Volume flow is computed by integrating the out-of-plane flow over the vessel cross-section. The algorithm was tested using a scattering-enhanced fluid in a 6.4-mm diameter dialysis tubing. For a wide range of transducer angles, the volume flow was accurately measured to within 28% in these preliminary tests.

Three-dimensional flow vectors from rf ultrasound signals

A new ultrasound technique for determining three-dimensional velocity vectors has been devised using radio frequency (RF) data from commercially available scanners. Applied to blood flow, this technique could prove useful for evaluating hemodynamics and detecting stenoses. Three orthogonal velocity vectors are computed from the RF signals of two steered beams from a single array. The in-plane velocities are determined using standard Doppler analysis, while the out-of-plane component is derived from the total velocity as computed from temporal decorrelation and the in-plane components. The technique was tested using contrast agent pumped through a flow tube. A GE Vingmed SystemV scanner with a 10 MHz linear array provided scans at beam steering angles of +/- 20 degree(s). Both Doppler velocities and temporal complex decorrelation were computed for each digitized voxel. Additional studies were done on a blood mimicking fluid and in vivo with a canine femoral artery. Vector plots were constructed to show flow for various transducer angles. Angle estimates were within 20 degree(s), and the mean error for the velocity amplitude was less than 15%. The in vivo results provided velocity estimates consistent with the literature. The proposed method, unlike current Doppler velocity measurement techniques, provides quantitative velocity information independent of transducer orientation.

3D compounding of B‐scan ultrasound images

Ultrasound imaging compounded from different look directions can significantly decrease speckle noise and increase structural contrast. In addition, current limits on the field of view from small aperture scanheads can be overcome by combining two or more sets of partially overlapping 3D scan volumes into one super‐volume by spatially coregistering the overlapping portions. The purpose of this study was to demonstrate both of these compound imaging enhancements. A 1.5‐D linear array was used to obtain overlapping ultrasound volumes in phantoms and test subjects, reconstructed from at least 60 parallel B‐scan planes for each volume. In the cases where independent look directions were required, either the transducer was tilted or the scan direction was changed. In all cases, the overlapping volumes were coregistered using an automated procedure based on a mutual information (MI) metric. The algorithm accounts for different look directions and/or tissue motion by geometrically transforming one volume set suc...

Volume flow measurement using Doppler RF decorrelation

A technique for monitoring volumetric flow was developed by combining standard Doppler measurements with amplitude decorrelation. The proposed algorithm uses current clinical ultrasound technology and is independent of vessel orientation. However, to accurately measure the ultrasound signals’ temporal decorrelation in blood, a contrast agent was added to increase the scattering signal strength. The algorithm uses standard frequency shifted Doppler signals, steered at two different angles, to determine the in‐plane velocities. For the same firing lines, the corresponding temporal amplitude decorrelation is related to total velocity. The velocity normal to the imaging plane can then be extracted and integrated to compute total volume flow. The algorithm was tested in a flow tank using a GE Logiq 700 clinical scanner with a 7.5 MHz linear array. The output power was set at the lowest level to reduce effects from additional decorrelation due to acoustic radiation force. RF data were collected as in‐phase and ...

Effect of spectacular reflection on out-of-plane ultrasonographic images reconstructed from three-dimensional data sets.

The effect of specular reflection on ultrasonographic images reconstructed out of plane to the plane of acquisition of a three‐dimensional volumetric data set was studied using two in vitro phantoms that incorporated structures exhibiting specular reflection. The phantoms were scanned transversely (axially) to form three‐dimensional data sets, with coronal cross‐sectional images reconstructed perpendicular to the plane of acquisition of the data sets. Directly scanned, nonreconstructed coronal images of the phantoms also were obtained in the same planes and from the same areas as the reconstructed coronal images. The direct and reconstructed coronal images were compared. Owing to the inherent directionality of specular reflectors, the reconstructed coronal images differed from the directly scanned images in two ways, containing some hyperechoic regions that were not present at direct coronal scanning and failing to contain other hyperechoic areas that were present at direct coronal imaging. We conclude that sonographic images reformatted from volumetric data sets may have a different appearance than images scanned directly in the same plane, independent of other factors such as resolution. This should be taken into account when such reformatted images are interpreted.

Image‐based calculation of elevational B‐scan separation

A speckle decorrelation technique was extended to high‐frequency imaging to calculate the elevational (out of plane) separation of B‐scan images. Pure speckle images were obtained with a 13‐MHz, 1.5‐D array in an elevational sweep over a phantom in 25‐μm steps. For each pixel the plane‐to‐plane autocorrelation function was computed for a number of frames and fit to a Gaussian to find the depth‐dependent scaling factor between the rate of speckle decorrelation and the actual frame spacing. From this the frame separation in sets of images containing speckle and structure was determined. To avoid using specular signals the mean intensity over standard deviation was employed to automatically detect areas of speckle. Based on the speckle decorrelation in these regions and using a 200*300 pixel subimage the frame spacing (100 μm) was calculated with 2% accuracy. The error increased with decreasing number of pixels and increasing separation of the frames. The technique can now be combined with high frame rate te...